The present invention relates to a drill for use in oil and gas drilling operations.
Drills have been proposed for gas and oil drilling which comprise multi-sectioned drill strings extending from the ground surface and carrying a cutter bit at the lower end. Rotary drive forces are applied to the drill string at the ground surface and are transmitted along the drill string to rotate the cutter bit. Not only are relatively large expenditures of energy required to rotate the entire drill string, but it is necessary to raise and uncouple every section of drill string in order to periodically replace the cutter bit. Furthermore, in the event that a break occurs along the length of the drill string, it is very difficult, if not impossible, to retrieve the string.
It has been heretofore proposed to eliminate the need for a drill string by utilizing a self-propelled cutter head which drills into the ground by means of a cutter head driven by a power plant carried by the head. The cutter head may comprise a plurality of telescoping sections, each carrying extensible/retractible shoes for engaging the wall of the hole being drilled. In this manner, one of the telescoping sections can be held fixed while the other section extends or retracts, and vice-versa, to enable the cutter head to "walk" down the hole in order to power the cutter bit. The power plant powers the cutter bit and is supplied with energy from the surface, such as electrical power or pressurized fluid, for example. Examples of such self-propelled heads are disclosed in U.S. Pat. No. 2,473,537 issued June 21, 1949; U.S. Pat. No. 2,643,087 issued June 23, 1953; U.S. Pat. No. 3,173,501 issued Mar. 16, 1965; U.S. Pat. No. 3,185,225 issued May 25, 1965; U.S. Pat. No. 3,232,362 issued Feb. 1, 1966; U.S. Pat. No. 3,407,887 issued Oct. 29, 1968; U.S. Pat. No. 3,882,946 issued May 13, 1975; U.S. Pat. No. 4,060,141 issued Nov. 29, 1977; and U.S. Pat. No. 4,143,722 issued Mar. 13, 1979.
Among the difficulties connected with the utilization of such self-propelled cutting heads is the need to dispose a practicable high-energy power plant within the limited amount of space available on the cutter head. Various proposals in this area involve the use of a drive mechanism disposed coaxially within the head, such as large turbine, a large hydraulic motor, or a group of series-connected electric motors, for example. While electrical power is simpler to supply than other forms of energy, it presents a serious heat dissipation problem within the drilling head. Fluid-actuated mechanisms such as turbines and hydraulic motors require that provision be made for supplying and withdrawing a continuous flow of pressurized fluid, thereby complicating the efforts to simplify and streamline the apparatus.
The use of a large coaxial fluid actuated mechanism maximizes the cross-sectional dimension of the drilling head, thereby further hindering streamlining efforts and, in the case of turbines, complicating the ability to conduct the spent hydraulic fluid upwardly from the bottom of the turbine.
It is, therefore, an object of the present invention to minimize or obviate problems of the type discussed above.
Another object of the invention is to provide a self-propelled drilling head which is of minimal cross-sectional dimension.
It is an additional object of the invention to provide a powerful space-saving drive mechanism for the cutter bit.
It is yet another object of the invention to provide an efficient drive train for transferring power efficiently and smoothly from the drive motors to the cutter bit.
It is a further object of the invention to provide a self-propelled drilling head of the step-down type which employs hydraulic fluid and effectively supplies and returns hydraulic fluid through the head by conduits which occupy minimal space.
A further object of the invention is to provide a self-propelled cutter head in which the components are safely shielded within rigid housings.